This invention relates to a novel process for the brazing of radiator cores all the parts thereof are made of aluminium or aluminium alloys and a part at least thereof are plated with a brazing alloy.
The invention relates to a non-stop brazing process, which means that the cores to be brazed are moved according to a strictly continuous motion or according to an intermittent but regular motion, and this with the use of hot gas instead of dipping the radiator cores into a melting salt bath.
Brazing by means of hot gas entails however some inconveniences which are well known. As a matter of fact, hot gas used must never be at a temperature above melting temperature of aluminium. Now, melting temperature of brazing alloys, particularly that of silicon-aluminium, is about the same as that of aluminium melting temperature (difference of about 30.degree. to 40.degree.C). On account of this small difference between the respective melting temperatures of aluminium and of brazing alloys thereof, the heating of parts, about the end of the heating, tends to an asymptote so that the end of the heating stage has to be long in order to reach regularly the brazing temperature.
It has been verified that the keeping of thin aluminium parts at a temperature close to brazing temperature is prejudicial to the making of good brazings, due to the flux covering inevitably the parts to be brazed is quickly damaged at high temperatures and there is a great risk that aluminium will reoxidate as a result of high temperature and the presence of oxygen in the hot gas.
Because of the large number of soldering joints involved in the manufacture of a radiator -- a few hundreds or even a few thousands -- it is also essential that all the joints be perfectly made, which requires that all the radiator parts in process of brazing be heated, at the same time, at the same temperature.
Another serious inconvenience lies in the fact the brazing being carried out at a temperature close to the melting temperature of aluminium, it follows that the metal when at a temperature close to said soldering temperature shows only extremely low strength characteristics, while, besides, all the radiator parts must remain pressed one against each other. Thereby, radiator manufacturers were heretofore fixed on the horns of the following dilemna: either tighten the parts and run the risk of the strain thereof when the metal softens, or to leave the parts loose which will not still prevent the straining thereof, and, consequently, to be no longer in contact one against the other which, as a result, making impossible the working out of brazing joints.
This problem becomes more complicated also with the expansion the core parts are subjected to, when heated at brazing temperature. Said expansion is, in fact, important and tends to create a play between the parts.
Another difficulty lies in the fact that the core, which must be tightened in a fitting, is necessarily in contact with said fitting. The holding fitting having to be rigid at brazing temperature is thus necessarily thick and the heating thereof, apart from the fact of its cost, is slow as compared with that of the core which results in the cooling of the core areas in contact with said fitting and a risk of faulty soldering close to said areas notwithstanding a tendency for the flux covering them to flow out towards the warmer parts of the core, where it may overflow and thereby pour too much soldering alloy into the aluminium which may perforate certain parts of the pieces. Moreover, the amount of flux may then be insufficient on certain areas of the parts.
The invention has been conceived and developed to provide means for brazing radiator cores with high efficiency and to ensure an improved brazing of all the joints.
According to the invention, the radiator cores, after being covered with flux, are moved into the successive areas of an enclosure, contiguous streams of hot gas directed at right angles to the front surface of said radiators are blown into each of said areas so as to create by themselves aerodynamic deflectors for the travelling of said streams in all the parts thereof, the velocity of a hot gas stream in one of the areas forming a pre-heating area is adjusted so as said velocity is just under the velocity limit at which the flux would be blown and carried away, the velocity of the hot gas stream in the next area wherein the cores are heated at soldering temperature is adjusted at a higher velocity than that prevailing in the pre-heating area, and one other area at least is arranged wherein the cores are cooled down at a temperature ranging about 300.degree.C before they are withdrawn from the enclosure.
The practical implementing of the invention has disclosed that additional inconveniences had to be overcomed. In particular, the moving of the radiator cores requires a travelling device capable of supporting the heat of the successive gas streams, as well as the corrosion resulting from flux vapours or being at least partly protected from said vapours. Moreover, the operation of said travelling device must obviously not disturb the travelling of said gas streams and the leakages of the latter must also be as low as possible.
This invention also answers this problem and provides an equipment for the implementing of this process.
According to this second provision of the invention, the equipment includes a number of cells externally similar as concerns the width and the height thereof, said cells including, in the aperture of the frame they delimit, two sole-plates or pillar-plates substantially parallel, one of which is fixed and the other is movable so as it may travel cross-wise to the lengthwise direction thereof, the front parts opposite said sole-plates or pillar-plates being fitted with thin edge projections between which the radiator core is gripped, so that said cores are only connected to said cell pillar-plates at a certain distance from said pillar-plates and so that by means of spot junctions leaving clear the whole of the front surface thereof, said cells being suspensed and moved in an air furnace including at least at the inlet and the outlet thereof a chamber locked by the cells upon the passage thereof, said furnace being connected with separated blowing and exhausting means for at least three air streams having different velocities and delimiting pre-heating, brazing and precooling areas which are connected between them without break of continuity.